lvm is great for creating logical volumes for vps installations on xen. i created a snapshot for doing a backup of one of the vps systems from domain-0, then when i was done, i tried to remove the snapshot with lvremove and the command never finished. later, i found out that any kernel after 2.6.15 requires lvm greater than 2.01 and devmapper greater than 1.01 to avoid such an uninterruptible hang.
here's some info about how i created the snapshot and recovered from the hang error.

here's the setup that led to the problem:
kernel 2.6.16.33-xen running on a debian sarge distro.
lvm2 from sarge installed the following:
lvm2_2.01.04-5_i386.deb
lvm-common_1.5.17_i386.deb
libdevmapper1.01_2%3a1.01.00-4sarge1_i386.deb